title: Posterior corneal elevation and back difference corneal elevation in diagnosing forme fruste keratoconus in the fellow eyes of unilateral keratoconus patients.
abstract: OBJECTIVE
  To evaluate posterior corneal elevation and back difference corneal elevation in patients with keratoconus in 1 eye and forme fruste keratoconus in the fellow eye.
  
  
  METHODS
  Kudret Eye Hospital, Ankara, Turkey.
  
  
  METHODS
  Case-control study.
  
  
  METHODS
  This study retrospectively reviewed patients with keratoconus in 1 eye and forme fruste keratoconus in the fellow eye and eyes of normal subjects. All subjects were evaluated with a rotating Scheimpflug imaging system (Pentacam), including sagittal and tangential anterior curve analysis, keratometry, and posterior elevation. The back difference elevation values were extrapolated from the difference maps of the Belin-Ambrosió enhanced ectasia display of the Scheimpflug system. The receiver operating characteristic (ROC) curves were analyzed to evaluate the sensitivity and specificity of the parameters.
  
  
  RESULTS
  The corneal power, pachymetric progression index, and posterior corneal elevation (posterior elevation and back difference elevation) measurements were statistically significantly higher in eyes with keratoconus or forme fruste keratoconus than in eyes of normal control subjects (P<.05). Using ROC analysis, the area under the curve values of mean keratometry, steepest point on the tangential curve, minimum corneal thickness, pachymetric progression index, Ambrósio's relational thickness, posterior elevation, and back difference elevation to distinguish forme fruste keratoconus from control subjects were 0.51, 0.84, 0.65, 0.81, 0.72, 0.68, and 0.76, respectively.
  
  
  CONCLUSIONS
  Back difference elevation was better than posterior elevation in diagnosing forme fruste keratoconus. However, as sole parameters, both had limited sensitivity and specificity to differentiate between forme fruste keratoconus eyes and normal control eyes.
authors.affiliation: Department of Ophthalmology (Muftuoglu), Medipol University, Istanbul, Turkey. orkunm@yahoo.com
authors.forename: Orkun
authors.initials: O
authors.lastname: Muftuoglu
authors.forename: Orhan
authors.initials: O
authors.lastname: Ayar
authors.forename: Kemal
authors.initials: K
authors.lastname: Ozulken
authors.forename: Erhan
authors.initials: E
authors.lastname: Ozyol
authors.forename: Arsen
authors.initials: A
authors.lastname: Akıncı
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D063171:Corneal Pachymetry; D019781:Corneal Topography; D004108:Dilatation, Pathologic / Q000175:diagnosis; D004728:Endothelium, Corneal / Q000473:pathology*; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis*; D008875:Middle Aged; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D055815:Young Adult